Apparatus for acquiring responsibility of oxygen concentration sensor

Abstract

The fact that “with respect to a process in which the output value of a downstream air-fuel ratio sensor (sensor output value) is inverted from the minimum output value to the maximum output value during execution of an active control, the local maximum and minimum values of the secondary differential value of the sensor output value is widely affected by the size of the response delay of the downstream air-fuel ratio sensor and the size of the degree of the degradation of the three-way catalyst” is utilized. By preliminarily acquiring and memorizing, as maps, these relations obtained through an experiment, and applying the “local maximum and minimum values of the secondary differential value of the sensor output value” calculated from the transition of the sensor output value acquired during execution of the active control to the maps, the response delay (time constant) of the downstream air-fuel ratio sensor is acquired.

What is claimed is: 
     
       1. An apparatus for acquiring the responsibility of an oxygen concentration sensor comprising:
 a three-way catalyst disposed in an exhaust channel of an internal combustion engine, 
 an electromotive force-type oxygen concentration sensor disposed below said three-way catalyst in said exhaust channel to generate an output value corresponding to the air-fuel ratio in the exhaust gas flowing out of said three-way catalyst, 
 an air-fuel ratio control means to control the air-fuel ratio in the exhaust gas flowing into said three-way catalyst, 
 a calculation means to calculate local maximum and/or minimum values in the secondary or more differential value with respect to time of said output value in a first case wherein, by adjusting said air-fuel ratio to a rich air-fuel ratio, which is richer than the theoretical air-fuel ratio, by means of said air-fuel ratio control means, the output value of said oxygen concentration sensor transitions so as to be inverted from a first predetermined value, which corresponds to an air-fuel ratio leaner than the theoretical air-fuel ratio, to a second predetermined value, which corresponds to an air-fuel ratio richer than the theoretical air-fuel ratio and is larger than said first predetermined value, or local maximum and/or minimum values in the secondary or more differential value with respect to time of said output value in a second case wherein, by adjusting said air-fuel ratio to a lean air-fuel ratio, which is leaner than the theoretical air-fuel ratio, by means of said air-fuel ratio control means, the output value of said oxygen concentration sensor transitions so as to be inverted from said second predetermined value to said first predetermined value, and 
 a responsibility acquisition means to acquire the responsibility of said oxygen concentration sensor based on said calculated local maximum and/or minimum values. 
 
     
     
       2. An apparatus for acquiring the responsibility of an oxygen concentration sensor comprising:
 a three-way catalyst disposed in an exhaust channel of an internal combustion engine, 
 an electromotive force-type oxygen concentration sensor disposed below said three-way catalyst in said exhaust channel to generate an output value corresponding to the air-fuel ratio in the exhaust gas flowing out of said three-way catalyst, 
 an air-fuel ratio control means to control the air-fuel ratio in the exhaust gas flowing into said three-way catalyst, 
 a calculation means to calculate, as a first extremum, a local minimum value in the secondary differential value with respect to time of said output value in a first case wherein, by adjusting said air-fuel ratio to a rich air-fuel ratio, which is richer than the theoretical air-fuel ratio, by means of said air-fuel ratio control means, the output value of said oxygen concentration sensor transitions so as to be inverted from a first predetermined value, which corresponds to an air-fuel ratio leaner than the theoretical air-fuel ratio, to a second predetermined value, which corresponds to an air-fuel ratio richer than the theoretical air-fuel ratio and is larger than said first predetermined value, or a local maximum value in the secondary differential value with respect to time of said output value in a second case wherein, by adjusting said air-fuel ratio to a lean air-fuel ratio, which is leaner than the theoretical air-fuel ratio, by means of said air-fuel ratio control means, the output value of said oxygen concentration sensor transitions so as to be inverted from said second predetermined value to said first predetermined value, and 
 a responsibility acquisition means to acquire the responsibility of said oxygen concentration sensor based on said calculated first extremum. 
 
     
     
       3. An apparatus for acquiring the responsibility of an oxygen concentration sensor according to  claim 2 , wherein:
 said responsibility acquisition means comprises a memorizing means to memorize a preliminarily acquired relation between the responsibility of said oxygen concentration sensor and said first extremum obtained in said first case or said second case, and is configured so as to acquire the responsibility of said oxygen concentration sensor based on said calculated first extremum and said memorized relation. 
 
     
     
       4. An apparatus for acquiring the responsibility of an oxygen concentration sensor according to  claim 3 , wherein:
 said memorizing means is configured so as to memorize said relation for each of multiple cases where the degradation degree of said three-way catalyst are different. 
 
     
     
       5. An apparatus for acquiring the responsibility of an oxygen concentration sensor comprising:
 a three-way catalyst disposed in an exhaust channel of an internal combustion engine, 
 an electromotive force-type oxygen concentration sensor disposed below said three-way catalyst in said exhaust channel to generate an output value corresponding to the air-fuel ratio in the exhaust gas flowing out of said three-way catalyst, 
 an air-fuel ratio control means to control the air-fuel ratio in the exhaust gas flowing into said three-way catalyst, 
 a calculation means to calculate, as a first extremum, a local minimum value in the secondary differential value with respect to time of said output value in a first case wherein, by adjusting said air-fuel ratio to a rich air-fuel ratio, which is richer than the theoretical air-fuel ratio, by means of said air-fuel ratio control means, the output value of said oxygen concentration sensor transitions so as to be inverted from a first predetermined value, which corresponds to an air-fuel ratio leaner than the theoretical air-fuel ratio, to a second predetermined value, which corresponds to an air-fuel ratio richer than the theoretical air-fuel ratio and is larger than said first predetermined value, or a local maximum value in the secondary differential value with respect to time of said output value in a second case wherein, by adjusting said air-fuel ratio to a lean air-fuel ratio, which is leaner than the theoretical air-fuel ratio, by means of said air-fuel ratio control means, the output value of said oxygen concentration sensor transitions so as to be inverted from said second predetermined value to said first predetermined value, and to calculate, as a second extremum, a local maximum value in the secondary differential value with respect to time of said output value in the first case, or a local minimum value in the secondary differential value with respect to time of said output value in the second case, and 
 a responsibility acquisition means to acquire the responsibility of said oxygen concentration sensor based on said calculated first extremum and said calculated second extremum. 
 
     
     
       6. An apparatus for acquiring the responsibility of an oxygen concentration sensor according to  claim 5 , wherein:
 said responsibility acquisition means comprises a memorizing means to memorize a preliminarily acquired relation between the responsibility of said oxygen concentration sensor and said first extremum and said second extremum obtained in said first case or said second case, and is configured so as to acquire the responsibility of said oxygen concentration sensor based on said calculated first extremum, said calculated second extremum, and said memorized relation. 
 
     
     
       7. An apparatus for acquiring the responsibility of an oxygen concentration sensor according to  claim 6 , wherein:
 said memorizing means is configured so as to memorize said relation for each of multiple cases where the degradation degree of said three-way catalyst are different. 
 
     
     
       8. An apparatus for acquiring the responsibility of an oxygen concentration sensor according to  claim 1 , wherein:
 said calculation means is configured so as to switch said air-fuel ratio from said rich air-fuel ratio to said lean air-fuel ratio based on that the output value of said oxygen concentration sensor is inverted from said first predetermined value to said second predetermined value, to switch said air-fuel ratio from said lean air-fuel ratio to said rich air-fuel ratio based on that the output value of said oxygen concentration sensor is inverted from said second predetermined value to said first predetermined value, to calculate the maximum oxygen storage capacity, which is the maximum value of the amount of oxygen that said three-way catalyst can absorb, every time when said air-fuel ratio is switched, as well as, to use, as said first case, a case where the output value of said oxygen concentration sensor transitions so as to be inverted from said first predetermined value to said second predetermined value in a condition where the degree of the discrepancy between the previous value and the current value of said calculated maximum oxygen storage capacity is judged as small, or, to use, as said second case, a case where the output value of said oxygen concentration sensor transitions so as to be inverted from said second predetermined value to said first predetermined value in a condition where the degree of the discrepancy between the previous value and the current value of said calculated maximum oxygen storage capacity is judged as small.